1. Field of the Invention
The present invention relates to powering of devices and communicating with devices through the same media.
2. Description of Related Art
Networks such as the Internet provide a variety of data communicated using a variety of network devices including servers, routers, hubs, switches, and other devices. Before placing a network into use, the network, including the network devices included therein, may be tested to ensure successful operation. Network devices may be tested, for example, to ensure that they function as intended, comply with supported protocols, and can withstand anticipated traffic demands.
To assist with the construction, installation and maintenance of networks and network devices, networks may be augmented with network analyzing devices, network conformance systems, network monitoring devices, and network traffic generators, all which are referred to herein as network testing systems. The network testing systems may allow for the sending, capturing and/or analyzing of network communications.
Power over Ethernet (PoE) technology allows IP telephones, wireless LAN access points, digital security cameras and other devices to receive power as well as data over existing LAN cabling, without needing to modify the existing Ethernet infrastructure. PoE is governed by the international standard, IEEE 802.3af, as an extension to the existing Ethernet standards.
The PoE standard dictates the power behavior of PoE devices (“Powered Devices,” or PDs) and the power supplies to which they are connected (“Power Sourcing Equipment,” or PSE). However, these dictates are not comprehensive.
One aspect of PoE is a requirement to prevent damage to existing Ethernet equipment. A “discovery process,” run from the PSE, examines the Ethernet cables, looking for PDs. It does this by applying a small current-limited voltage to the cable and checks for the presence of a 25 k ohm resistor in the remote device. Only if the resistor is present is the full voltage is applied, but this is still current-limited to prevent damage to cables and equipment in fault conditions.
The PD must continue to draw a minimum current. If it does not (for example, when the device is unplugged) then the PSE removes the power and the discovery process begins again.
As an optional extension to the discovery process, a PD may indicate to the PSE its maximum power requirements.
The PSE may optionally provide a level of system management, using, for example, the Common Management Interface Protocol (CMIP) or the Simple Network Management Protocol (SNMP). This allows, for example, PDs to be powered off at night, or remotely reset.